Yonkly is an open source twitter clone application built with ASP.net MVC. Yonkly provides the functionalities of twitter and some additional features such as threaded messages and also provides integration with twitter. Visit Emad Ibrahim's (Author of Yonkly) blog post for the detailed information. The project is available in Codeplex at http://www.codeplex.com/yonkly
Read the complete post at http://feeds.feedburner.com/~r/ShijuVBlog/~3/415520018/yonkly-an-open-source-twitter-clone-with-asp-net-mvc.aspx